Best practice Net Core Api and Docker - docker

Question

I'm trying to find over the net how to manage properly Dockerfile in order to make the best possible image, but unfortunately no good way appeared to me. That's why I ask here.
This is my context :
I'm developping Net Core 3 web API
I'm using template from VS2019
I'm using the original DockerFile with some modifications
Here is my Dockerfile :
#See https://aka.ms/containerfastmode to understand how Visual Studio uses this Dockerfile to build your images for faster debugging.
FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-buster-slim AS base
RUN apt-get update;apt-get install libfontconfig1 -y
WORKDIR /app
EXPOSE 80
EXPOSE 443
FROM mcr.microsoft.com/dotnet/core/sdk:3.1-buster AS build
WORKDIR /src
COPY ["Src/API/API.csproj", "Src/API/"]
RUN dotnet restore "Src/API/API.csproj"
COPY . .
WORKDIR "/src/Src/API"
RUN dotnet build "API.csproj" -c Release -o /app/build
FROM build AS publish
RUN dotnet publish "API.csproj" -c Release -o /app/publish
FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "API.dll"]
There is my solution structure :
.
| .dockerignore
| mySolution.sln
+---Docs
+---Src
| \---API
| | API.csproj
| | API.csproj.user
| | appsettings.Development.json
| | appsettings.json
| | appsettings.Staging.json
| | Dockerfile
| | Dockerfile.original
| | Program.cs
| | Startup.cs
| +---.config
| | dotnet-tools.json
| +---bin
| +---Controllers (source files)
| +---Data (source files)
| +---Database (source files)
| +---Dtos (source files)
| +---Helpers (source files)
| +---Mail (source files)
| +---Migrations (EF source files)
| +---Models (source files)
| +---obj
| +---PDF (source files)
| +---Properties
| | | launchSettings.json
| +---Services (source files)
| \---wwwroot
| +---Templates
| \---uploads
\---Tests
As you can see, if I want to build my image without VS2019, I have to put the Dockerfile to the root directory (where is the .sln file is).
For now, if I use this Dockerfile, Docker will copy all files / directories from Src directory, including bin / obj directories, and wwwroot directory which can contains some files from my upload tests.
If I check in Visual Studio the file structure in my container :
As you can see, I don't need to all files, only my sources in order to build and deploy my app.
How can I upgrade my Dockerfile in order to make the most proper image ?

Answer 1

Some tips:
For security/portability use alpine instead of buster slim in the final image.
At the final image, use "USER NOBODY" to run Dockerfile as non-root.
That will require usage of ports above 1024.
For the building purpose control the current context using '-f' so you can leave Dockerfile inside but use context from solution root and even if you have CI/CD pipelines.
Run your unit tests inside Dockerfile before last stage so if it fails, it would stop.
Think about secrets and that depends where you will run your container because AppConfigs aren't recommended.